In aircraft, in particular commercial aircraft, the demand for a high cruising speed as well as for a low take-off and landing speed is given, which rises the necessity of high lift systems, which can be activated during take-offs and landings to increase a lift coefficient. This is generally accomplished with lift-increasing devices, which are deflected into the airstream of the aircraft. Examples of such lift-increasing devices are extendable forward leading slats, such as Krueger slats, or rear trailing flaps, which are arranged so that they can be moved relative to the aircraft wing.
In an extended position, slats can be spaced or offset from the leading edge of the aircraft wing, thereby forming a gap relative to the leading edge of the aircraft wing. The gap allows an energy-rich stream of air to move from the flow approaching the aircraft wing onto the upper profile side of the aircraft wing, where it shifts the stall towards higher angles of attack. Depending on the design, slats can be deflected with or without forming a gap in the flow approaching the aircraft wing, and increase both the surface of the aircraft wing and its curvature.
Document DE 10 2010 014 792 A1 relates to a high lift system for an aircraft. To ensure that the aircraft wing contour comprises a contour optimized for cruise flight with the Krueger-slat in a retracted position, the aircraft wing comprises a depression for accommodating the Krueger-slat, wherein the shape of the Krueger-slat and the depression in the aircraft wing are adjusted to each other. In its retracted position, the Krueger-slat is in an “upside down” position, since the rear trailing edge of the Krueger-slat is in front of the forward leading edge of the Krueger-slat. In other words, the upper surface of the Krueger-slat forms a part of the lower surface of the aircraft wing, when being in its retracted position. In order to increase the lift coefficient during take-offs or landings, the Krueger-slat has to be rotated from the “upside down” position to an “upside up” position to reach an operating position, where the Krueger-slat is spaced or offset from the leading edge of the wing, thereby increasing the lift coefficient.
One problem associated with the deployment of the aforementioned Krueger-slat is that when such a Krueger-slat is swung from the retracted, “upside down” position to the operating, “upside up” position, the Krueger-slat is pivoted downwardly into the airstream and therefore is temporarily positioned broadside in the airstream. One disadvantage of this swing movement of the Krueger-slat is that the power requirements for deploying the Krueger-slat are relatively high.
Document U.S. Pat. No. 4,202,519 relates to an airfoil leading edge slat apparatus, which is configured to move the slat initially downward and forward and thereafter forward and upward, such that the slat is elevated above the front leading edge of the aircraft wing. One problem associated with this apparatus is still that a surface of the slat, now the lower surface of the slat, forms a part of the lower surface of the aircraft wing. Thus, the lower surface of the slat is not free in shape. One further disadvantage of this approach is that a part of the drive mechanism configured to drive the slat between the retracted position and the operating position is arranged outside the aircraft wing and therefore provides an increased air drag even during cruise configuration.